1. Field of the Invention
The present invention relates to an actinic-ray- or radiation-sensitive resin composition employed in a semiconductor production process for an IC or the like, a circuit board production process for a liquid crystal, a thermal head or the like and other photoapplication lithography processes, and also relates to a method of forming a pattern with the use of the composition. More particularly, the present invention relates to an actinic-ray- or radiation-sensitive resin composition that is suitable for exposure by means of a liquid-immersion projection exposure unit using far-ultraviolet rays of wavelength 300 nm or shorter as a light source, and also relates to a method of forming a pattern with the use of the composition.
In the present invention, the terms “actinic rays” and “radiation” mean, for example, a mercury lamp bright line spectrum, far-ultraviolet rays represented by an excimer laser, extreme ultraviolet rays, X-rays, electron beams and the like. In the present invention, the term “light” means actinic rays or radiation.
2. Description of the Related Art
In accordance with the miniaturization of semiconductor elements, the wavelength shortening of the exposure light source and the realization of high numerical apertures (high NA) for projector lenses have been advanced. At present, an exposure machine of 0.84 NA using an ArF excimer laser of wavelength 193 nm as a light source has been developed. As is commonly known, the following formulae can be established therefor.(Resolving power)=k1·(λ/NA)(Focal depth)=±k2·λ/NA2 
In the formulae, λ is the wavelength of the exposure light source; NA is the numerical aperture of the projector lens; and k1 and k2 are factors relating to the process.
As a technology for enhancing the resolving power of an optical microscope in order to attain a further resolving power enhancement by wavelength shortening, it is heretofore known to employ a liquid immersion technique, that is, a method in which a space between a projector lens and a sample is filled with a liquid of high refractive index (hereinafter also referred to as a “liquid for liquid immersion”).
The “effect of the liquid immersion” is as follows. Taking λ0 as the wavelength of exposure light in air, n as the refractive index of the liquid for liquid immersion to air and θ as the convergent half angle of the light beam, where NA0=sin θ, the above-mentioned resolving power and focal depth in the event of liquid immersion can be expressed by the following formulae.(Resolving power)=k1·(λ0/n)/NA0 (Focal depth)=±k2(λ0/n)/NA02 
That is, the effect of the liquid immersion is equivalent to the use of an exposure wavelength of 1/n.
In other words, in projection optic systems of identical NA, the liquid immersion would enable the focal depth to be n-fold.
This is effective in all pattern configurations. Further, this can be combined with a super-resolution technology, such as a phase shift method or a modified illumination method, now under study.
Examples of the apparatuses utilizing this effect in the transfer of the microscopic image pattern of a semiconductor element are introduced in patent references 1, 2, etc.
The recent progress of the liquid immersion exposure technology is reported in non-patent references 1, 2, 3, etc. In the use of an ArF excimer laser as a light source, it is presumed that pure water (refractive index at 193 nm: 1.44) can offer most promising prospects as the liquid for liquid immersion from the viewpoint of handling safety as well as 193-nm transmission and refractive index.
Since the emergence of the resist for a KrF excimer laser (248 nm), an image forming method through chemical amplification has been employed as a resist image forming method in order to compensate for any sensitivity deterioration caused by light absorption. Brief description of an image forming method through positive chemical amplification is given below by way of example. Upon exposure, an acid generator will be decomposed at exposed areas to thereby generate an acid. In baking after the exposure (post-exposure bake [PEB]), the generated acid is used as a reaction catalyst so that an alkali-insoluble group is converted to an alkali-soluble group. Thereafter, alkali development is carried out to thereby remove the exposed areas. Thus, the relevant image forming method is provided.
The resist for an ArF excimer laser (193 nm) utilizing this chemical amplification mechanism is now becoming mainstream. However, in the liquid immersion exposure, the resist has been unsatisfactory in the problem of pattern collapse such that a formed line pattern collapses to thereby cause a defect in device production and in the problem of line edge roughness involving roughening of pattern side walls.
Further, it is pointed out that when the chemical amplification resist is applied to the liquid immersion exposure, as the resist layer is brought into contact with the liquid for liquid immersion at the time of exposure, not only would the resist layer suffer a property alteration but also a component having an unfavorable influence on the liquid for liquid immersion would leach from the resist layer. Patent reference 3 describes an instance of resist performance alteration by immersing a resist for ArF exposure in water before and after the exposure, and in the reference this is noted as being a problem in liquid immersion exposure. Patent reference 4 describes an instance of suppressing the above-mentioned leaching by the addition of a siliconized or fluorinated resin.
Moreover with respect to the liquid immersion exposure process, when exposure is carried out using a scan type liquid immersion exposure machine, the exposure speed would be lowered by a failure of the liquid for liquid immersion to move while following a moving lens. An unfavorable influence thereof on the productivity is apprehended. When the liquid for liquid immersion is water, it is preferred for the resist film to be hydrophobic from the viewpoint of superiority in water following properties.
[Prior Art Literature]
[Patent Reference]    [Patent reference 1] Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 57-153433,    [Patent reference 2] JP-A-7-220990,    [Patent reference 3] International Publication WO/2004/068242, and    [Patent reference 4] JP-A-2006-309245.
[Non-Patent Reference]    [Non-patent reference 1] Proc. SPIE, 2002, Vol. 4688, page 11,    [Non-patent reference 2] J. Vac. Sci. Tecnol. B 17 (1999), and    [Non-patent reference 3] Proc. SPIE, 2000, Vol. 3999, page 2.